Fuel gauge for an automotive vehicle

ABSTRACT

A fuel gauge is so designed that a fuel level signal having a signal value responsive to the fuel amount in a fuel tank is averaged over time intervals which vary according to whether the liquid level of the fuel in the tank is stable or unstable and a fuel quantity is calculated and displayed according to the averaged value. The stable or unstable condition of the fuel level is discriminated in accordance with vehicle speed, the &#34;on&#34; or &#34;off&#34; position of an ignition switch or the like. Accordingly, when the fuel level is unstable, the signal value is averaged over a time interval which is longer than that used when the fuel level is stable so that the response of display to variation of the fuel level is improved.

FIELD OF THE INVENTION

This invention relates to a fuel gauge for an automotive vehicle, andmore particularly, a fuel gauge which is so designed that thefuel-measuring timing is varied in accordance with driving conditions ofthe automotive vehicle.

In conventional art, fuel gauges which measure the amount of fuelremaining in a fuel tank of a vehicle are well known. One typicalconventional fuel gauge is designed so as to average a detectedfuel-level signal to display the fuel amount. That is, since the fuel isapt to be agitated on account of the inertial forces applied to the fuelin the tank under certain conditions such as when the vehicle movesthrough a curve, the vehicle is accelerated or decelerated, or the like,it is necessary to average the detected-fuel-level signal in order tomeasure the actual fuel amount. Such a fuel gauge which displays thefuel amount after performing the fuel level averaging operation, isconvenient for displaying the average fuel amount. However, since theresponse of the fuel gauge, that is, the response of display to avariety of fuel levels, is normally determined while the vehicle ismoving, this may possibly cause problems in the case of increase of thefuel level in the fuel tank within a short time, such as duringrefueling, in that the increment of fuel is displayed with delay. On theother hand, it is desirable to display the fuel amount at once when theignition key is turned to the accessory position in order to start thevehicle. However, if the averaging interval for the detected fuel-levelsignal is relative long, this may cause another problem in that the fuellevel display is delayed for a while when the ignition key is turned tothe accessory or ignition position.

On the other hand, as is well known, a fuel gauge including a float-typesliding resistor or a winding resistor generating an analog signal asthe detected-fuel-level signal comprises a float which floats on thesurface of the fuel and a brush which is adapted to slide along theresistor, and the float and the brush are assembled in a single body sothat the brush is moved as the float moves in accordance with variationsof fluid level. As a result, the resistance value of the slidingresistor or winding resistor varies. Thus, if a constant current issupplied to this resistor, the voltage will vary when the resistancevalue of the resistor varies. Accordingly, the fuel amount can bedisplayed by detecting the voltage variations. Since the voltage valuegenerated by the fuel gauge varies in accordance with the variation ofthe fuel level owing to the vibration or shaking of vehicle while thevehicle is moving, the detected fuel level signal is averaged by anintegrator so that the fluctuation of voltage while the vehicle ismoving is smoothed. However, this requires an averaging time of about 1to 2 minutes. Thus, the display may appear with a delay of about 1 to 2minutes after the ignition key is turned to the accessory or ignitionposition, or after the vehicle starts from a dead stop.

With these problems in mind, it is an object of the present invention toover come these problems by switching the averaging interval of thedetected-fuel-level signal in accordance with vehicle conditions; thatis, the fluctuation of detected fuel-level signal is decreased by usinga relative long averaging interval in the case when the vehicle ismoving, and the response of the fuel-level display is improved bymeasuring the detected fuel-level signal with a relatively shortaveraging interval in cases when the vehicle is supplied with fuel orjust before the engine is started.

SUMMARY OF THE INVENTION

To accomplish the above described object or other objects, a fuel gaugeaccording to the present invention comprises means for generating asignal having a value representative of the fuel level in a fuel tank,means for calculating and displaying the fuel level in the fuel tank inaccordance with the signal value, and means for discriminating vehicledriving conditions in accordance with predetermined parameters andchanging the timing of the calculation and display the fuel level inaccordance with the discriminated conditions. Thus, according to thefuel gauge of the present invention, the response characteristics tovariation of the fuel level in the fuel tank can be improved and themeasured result can be more accurate by changing the timing inaccordance with vehicle driving conditions. As a result, the fuel gaugehas superior reliability and improved response characteristics incomparison with conventional fuel gauges.

According to a preferred embodiment of the present invention, there isprovided a fuel gauge comprising a fuel level detecting means forgenerating a first signal having value variable in proportion to thefuel level in the fuel tank, an averaging means for averaging the signalvalues over a given period of time at a predetermined timing to producea second signal having a value representative of the averaged value, atiming control means for detecting vehicle driving conditions inresponse to variation of a predetermined parameter and changing theoperational timing of the averaging means in accordance with thedetected vehicle driving conditions, and a calculating means forcalculating the fuel level in the fuel tank in accordance with thesecond signal and displaying the calculated value.

In addition, according to a measuring method for measuring fuel, theresponse characteristics, fidelity to variation of the fuel level andaccuracy of measurement of the fuel level are improved by generating afirst signal having a value which corresponds to the fuel level in afuel tank, obtaining an average of fuel levels over a predetermined timeperiod by averaging the signal value of the first signal at apredetermined frequency, generating a second signal having a value whichcorresponds to the average fuel level, calculating the amount of fuel inthe fuel tank in accordance with the signal value of the second signal,discriminating vehicle driving conditions in accordance with a specificparameter, and varying the averaging frequency and the time interval forthe first signal in accordance with the discriminated result.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be understood more fully from the detaileddescription given herebelow and from the accompanying drawings of thepreferred embodiment of the present invention, which, however, shouldnot be taken as limitative to the invention but for explanation ofelucidation only.

In the drawings;

FIG. 1 is a block diagram of an embodiment of a fuel gauge according tothe present invention;

FIG. 2 is an illustrative view of a fuel level detector which is used ina fuel gauge of the embodiment of FIG. 1;

FIG. 3 is a circuit diagram of the fuel level detector shown in FIG. 2;

FIG. 4 is a block diagram of another embodiment of fuel gauge accordingto the present invention;

FIG. 5 is a block diagram of an other embodiment of fuel gauge accordingto the present invention; and

FIG. 6 is a flow chart of the fuel gauge shown in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a block diagram of a first embodiment of a fuel gaugeaccording to the present invention. A fuel gauge is inserted into a fueltank. The fuel gauge comprises a fuel level detector 10 outputting apulse signal S₁ (hereinafter referred to "fuel level pulse") thefrequency of which is variable in accordance with the fuel level, acalculation circuit 20 which derives the average period or frequency ofthe fuel level pulse S₁ within a predetermined time period andcalculates a fuel quantity in accordance with the derived averageperiod, and a display device 30 for displaying the fuel quantity inresponse to the calculated result of the calculation circuit 20. Thecalculation circuit 20 is futher connected to a vehicle speed sensor 40so that the calculation circuit adjusts the predetermined time periodfor deriving the average frequency depending upon presence or absence avehicle speed signal S₂ from the vehicle speed sensor.

As shown in FIG. 2 and FIG. 3, a level sensor 12 of the fuel leveldetector 10 used in this embodiment has a capacitor 104 which is adaptedto be inserted in a fuel tank 102. The capacitor 104 comprises a firstelement 106 and a second element 108. The first and second elements 106and 108 respectively consist of pairs of symmetrical flat plates 110,112 and 114, 116. The flat plates 110, 112 and 114, 116 of each pairfunction as conductive members of the capacitor. The flat plates 110,112and 114, 116 of each pair are arranged face to face and separated by apredetermined distance by a spacer (not shown) made of an insulatingmaterial. The first and second elements 106 and 108 are electricallyconnected via a harness 118, that is, the flat plates 110 and 114, and112 and 116 are connected, respectively. Accordingly, the totalcapacitance of the capacitor 104 corresponds to the sum of thecapacitances of the first and second elements.

The top 120 of the fuel tank 102 partially protrudes so as to form aprojecting portion 122 with a trapezoid profile in cross-section. Theprojecting portion 122 is formed with an opening 124. A casing for anoscillator 14, hereinbelow explained in detail, is housed in the opening124 of the projecting portion 122 and fixed via a fixing means, notshown. Each of the flat plates 110, 112, 114 and 116 is formed at thetop end with a projection 128, 130, 132 or 134. The plates 114 and 116forming the second element 106 are suspended in the fuel tank 102 andare insulated from one another by means of a suspending means, notshown. The flat plates 110 and 112 forming the first element 108 arefixed to the lower surface of the oscillator casing via the projections128, 130 so as to be insulated with respect to each other. In thismanner, the flat plates 110, 112, 114 and 116 are vertically arrangedwith respect to the liquid surface of the fuel in the tank 102.

In the above mentioned structure, since the fuel, such as gasoline, andair have different dielectric constants, the electrical capacity of thecapacitor 104 varies in accordance with the immersed area of the firstand second elements 106, 108. Accordingly, the electrical capacity ofthe capacitor 104 changes in response to the level of fuel.

As shown in FIG. 3, the oscillator 14 is an R-C oscillator, theoscillating frequency of which in accordance with the electrostaticcapacity of the capacitor 104, and which is connected to a power source+Vcc via potential-dividing resistors R₁ and R₂. Thus, in this case theoscillating frequency f produced by the oscillator 14 is determined bythe following equation; ##EQU1## wherein, r₁ respresents the resistanceof the resistor R₁,

r₂ represents the resistance of the resistor R₂,

c represents the electrostatic capacity of the capacitor 104.

The resistance values of R₁ and R₂ are preferably so determined that theoscillating frequency varies from 5 KHz to 10 KHz when the dielectricconstant ε of the fuel; i.e., regular gasoline, is represented byε=2×8.85×10⁻¹² F/m. The electrostatic capacity of the capacitor 104varies from 1000 pF to 2000 pF corresponding to the conditions fromempty to full of the tank.

A frequency divider 16 divides the oscillating signal S₃ from theoscillator 14 into 1/2⁶ thereof. The output from the frequency divider16 is input into the calculation circuit 20 as the fuel level pulse S₁.

The calculation circuit 20 includes first and second counters 22 and 24which respectively count different numbers of fuel level pulses S₁ fromthe fuel level detector 10 so as to obtain the average pulse period. Inthis embodiment, the first counter 22 obtains the average pulse periodby counting 500 pulses and outputs a counter pulse S₄ representing theaverage pulse period. On the other hand, the second counter 24 obtainsthe average pulse period by counting 10000 pulses and outputs a counterpulse S₅ representing the average period.

A switching circuit 28 is disposed between the first and second counters22 and 24, and the frequency divider 16. The switching circuit 28comprises a switching signal generator 282 which generates a switchingsignal S₆ in accordance with the vehicle speed signal S₂ from thevehicle speed sensor 40, and a switch 284 which connects the frequencydivider 16 to the second counter 24 in response to the switching signalS₆, or connects the frequency divider 16 to the first counter when theswitching signal S₆ is absent. Accordingly, when the vehicle stops, thefirst counter 22 determines the average pulse period based on 500 fuellevel pulses S₁ so that the counter pulse S₄ representing this averagepulse period is output. On the other hand, when the vehicle is running,the fuel level pulse S₁ output from the frequency divider 16 is inputinto the second counter 24 in which the average pulse period isdetermined by counting 10000 fuel level pulses so that the counterpulses S₅ are output.

The counter pulse S₄ or S₅ output from the first counter 22 or secondcounter 24 is input into a calculating unit 26. Since the calculatingunit 2 is storing a pulse period To (10 KHz=0.1 msec) generated when thefuel tank 102 is empty, the fuel quantity in the fuel tank 102 can beobtained by the following equation; ##EQU2## wherein; Q represents thefuel quantity (liter),

T represents the period of the counter pulse,

N represents the capacity of the fuel tank.

Then the calculation circuit 20 outputs an output signal S₇ having avalue corresponding to the fuel quantity according to the calculatedresult. The output signal S₇ from the calculation circuit 20 is outputin a form of a digital signal or analog signal in accordance with thenature of the display device 30, that is, depending on the display is adigital display system or an analog display system.

In the above mentioned embodiment, although the fuel amount iscalculated on the basis of the period of pulses, it may be alsocalculated according to the frequency of pulse. In addition, the vehiclespeed sensor 40 may be replaced by an ignition switch so that theswitcing signal may be generated by actuating the switching signalgenerator 282 in response to the "on" position of the ignition switch.

FIG. 4 shows another embodiment of the present invention, in which theelectrostatic-type fuel level detector is replaced by a fuel leveldetector 50 including a well-known float-type sliding resistor orwinding resistor which generates an analog signal indicative of the fuellevel. In this well-known fuel level detector 50, a brush moves alongthe sliding resistor or the winding resistor in accordance with thefloat level position so that the analog value of the detected signal S₁₀varies in accordance with the resistance value which varies according tothe movement of the brush. The detected signal S₁₀ from the fuel leveldetector 50 is input to either a first integrator 64 or a secondintegrator via a switch 622 of a switching circuit 62 in a calculationcircuit 60. The first and second integrators 64, 66 are provided withdifferent time constants. The time constant of the first integrator 64is chosen to be shorter than that of the second integrator. In thisembodiment, the time constant of the first integrator 64 is chosen to be4 to 6 seconds, and the second integrator 66, 60 to 90 seconds.

The switch 622 is connected to a switching signal generator 624 whichgenerates a switching signal S₁₁ while an ignition switch 70 is turnedon so that the input of the switching signal S₁₁ connects the secondintegrator 66 and the fuel level detector 50. When the switching signalis not generated, the first integrator 64 is connected to the fuel leveldetector 50. The integrator 64 or 66 calculates the average of thedetected values within the period of each respective time constant andthe result is output to a calculating unit 68 as an analog signal S₁₂.The calculating unit 68 calculates the fuel quantity according to theanalog signals S₁₂ and outputs an output signal S₁₃ corresponding to thecalculated result to a display device 80.

FIG. 5 show another embodiment according to the present invention, inwhich the calculation circuit is composed of a microcomputer 90. A fuellevel detector 92 outputs a fuel level pulse S₂₀ to an interface 902 ofthe microcomputer 90. In addition, the interface 902 is connected to avehicle speed sensor 94. RAM 904 of the microcomputer 90 is connected toa clock generator 96 which generates a clock signal S₂₁ and includes acounter I 906 for counting the clock signal pulses S₂₁ and a counter II908 for counting the fuel level pulses S₂₀ input via the interface 902.ROM 910 stores the following equations in order calculate an averagepulse period T of a predetermined number of fuel level pulses accordingto the counted values of the counter I 906 and counter II 908 calculatethe fuel amount according to the average pulse period T respectively##EQU3## where To represents the pulse period in the case that the fueltank is empty.

CPU 912 calculates the fuel quantity in the fuel tank in accordance withthe programs stored in ROM 910, and outputs the calculated result to adisplay device 98 via an output unit 914.

FIG. 6 is a flow chart of the operation of the microcomputer 90 in FIG.5, and the program is carried out continuously or at a predeterminedtiming. After the program starts, the counter I 906 and the counter II908 are set at the blocks 920 and 922, respectively. Then, the presenceor absence of the sensor signal S₂₂ from the vehicle speed sensor 94 ischecked at the block 924. If the sensor signal S₂₂ from the vehiclespeed sensor 94 is absent; that is, the vehicle speed is zero, "1" isadded to the counter II 908 in synchronism with the fuel level pulse S₂₀at the block 925, and then the counted value of the counter II 908 ischecked as to whether or not the value coincides with 500 at the block926. The blocks 924 and 926 are repeated until the counted value of thecounter II 908 coincides with this value so that 500 fuel level pulsesS₂₀ are counted. Concurrently, the counter I 906 is continuouslycounting the clock signal pulses S₂₁. When the counted values coincideswith 500 at block 926, the counted values from the counter I and thecounter II are read out at the blocks 928 and 930. Then the averagepulse period T is calculated according to the equation ##EQU4## at theblock 932. According to the calculated result from the block 932,##EQU5## is calculated at the block 934 and the output unit outputs theresultant value to the display device 98 at the block 936.

On the other hand, if the sensor signal S₂₂ from the vehicle speedsensor 94 is present at block 924, that is, if the vehicle is running ata non-zero speed, the block 938 and the block 940 are repeated. Thus,"1" is added to the counter II in synchronism with the fuel level pulseS₂₀ at the block 938. When the counted value of the counter II coincideswith 10,000, the processes at the block 928 et seq. are carried out soas to display the fuel amount on the display device.

As given in the explanation above according to the present invention,the response to variation of fuel quantity, particularly the response tovariation of the fuel quantity while the vehicle is stopped, can beimproved by varying the timing of the fuel quantity calculations inaccordance with the automotive vehicle driving condition.

What is claimed is:
 1. A fuel gauge for an automotive vehiclecomprising;first means for generating a first signal, the value of whichvaries in response to the fuel level in a fuel tank; second means forgenerating a second signal, the value of which is the average of thevalue of the above mentioned first signal over a first predeterminedlength of time; third means for generating a third signal, the value ofwhich is the average of the value of the above mentioned first signalover a second predetermined length of time; fourth means for actuatingalternatively the above mentioned second or third means in accordancewith the vehicle driving condition so as to allow the actuated means tooutput the corresponding one of said second and third signals; and fifthmeans for calculating a fuel quantity according to the value of theoutputted one of said the second and third signals and displaying thecalculated result.
 2. The fuel gauge according to claim 1, wherein theabove mentioned first predetermined length of time is significantlyshorter than the above mentioned second predetermined length of time. 3.The fuel gauge according to claim 2, wherein the above mentioned fourthmeans includes a vehicle speed sensor and actuates the above mentionedsecond means when the sensor does not generate an output, or the abovementioned third means when the sensor generates an output.
 4. The fuelgauge according to claim 2, wherein the above mentioned fourth meansincludes an ignition switch and actuates the above mentioned secondmeans when the ignition switch is turned off, or the above mentionedthird means when the ignition switch is turned on.
 5. An automotivevehicle characterized by comprising;a fuel level detecting means forgenerating a detected fuel-level signal corresponding to a fuel level;an averaging circuit having different selectable averaging times foraveraging the detected signal output from the detecting means; acondition discriminating means for discriminating the vehicle condition;a switching means for switching the averaging time of the abovementioned averaging circuit in accordance with the condition signaloutput from the condition discriminating means; a calculating means forcalculating a fuel quantity according to the detected signal averaged bythe above mentioned averaging circuit; and a display device fordisplaying the fuel amount output from the calculating means.
 6. Thefuel gauge according to claim 5, wherein the above mentioned conditiondiscriminating means comprises a vehicle speed sensor, and a switchingsignal generating means for outputting different condition signals inaccordance with the vehicle speed signal from the vehicle speed sensor.7. The fuel gauge according to claim 5, wherein the above mentionedcondition discriminating means comprises an ignition switch and aswitching signal generating means for outputting a different conditionsignal according to whether the switching position of the ignitionswitch is the "on" position or the "off" position.
 8. The fuel gaugeaccording to claim 5, 6 or 7, wherein the above mentioned detectedsignal is a pulse signal and the above mentioned averaging circuitaverages the periods of different numbers of pulse signals and outputs apulse signal indicative of the averaged pulse period.
 9. The fuel gaugeaccording to claim 5, 6 or 7, wherein the above mentioned detectedsignal is a pulse signal, and the above averaging circuit counts pulsesignals for different time intervals and outputs a pulse signal having afrequency corresponding to the averaged frequency within the abovementioned time interval.
 10. The fuel gauge according to claim 5, 6 or7, wherein the above mentioned detected signal is an analog signal, andthe above mentioned averaging circuit averages the analog signal overdifferent time constants and outputs a signal having the valueequivalent to the averaged value.
 11. A fuel gauge for an automotivevehicle comprising;a fuel level detecting means for generating a firstsignal, the value of which viries in response to the fuel quantity in afuel tank; an averaging means for averaging the above mentioned firstsignal at a predetermined timing and generating a second signal having avalue according to the averaged value; a timing control means fordetecting vehicle driving conditions according to the variation of apreselected parameter and changing the predetermined timing of the abovementioned averaging means in accordance with the driving conditions; anda calculating means for calculating the fuel quantity in the fuel tankaccording to the second signal and displaying the calculated result. 12.The fuel gauge according to claim 11, wherein the above mentioned timingcontrol means includes a vehicle speed sensor, and averages, inaccordance with the sensed vehicle speed, the value of the first signalover a first time interval when the vehicle speed is zero or the valueof the first signal over a second time interval which is longer than thefirst time interval when the vehicle is running at a non-zero speed. 13.The fuel gauge according to claim 11, wherein the above mentioned timingcontrol means includes an ignition switch and averages, using "on" or"off" position of the ignition switch as a parameter, the value of thefirst signal over a first time interval when the ignition switch is inthe "off" position or the value of the first signal over a second timeinterval which is longer than the first time interval when the ignitionswitch is in the "off" position.
 14. The fuel gauge according to claim11, 12 or 13, wherein the above mentioned first signal is a pulse signaland, the above mentioned averaging means averages different numbers ofpulse signals so as to output a pulse signal representing the averagedpulse period.
 15. The fuel gauge according to claim 11, 12 or 13,wherein the above mentioned first signal is a pulse signal and the abovementioned averaging means counts pulse signals for different timeintervals so as to output a pulse signal having a frequencycorresponding to the averaged frequency within the above mentioned timeinterval.
 16. The fuel gauge according to claim 11, 12 or 13, whereinthe above mentioned first signal is an analog signal, and the abovementioned averaging circuit averages the analog signal at different timeconstants so as to output a signal having a value equivalent to theaveraged value.
 17. A measuring method for measuring a fuel quantitycomprising;measuring continuously a fuel level in a fuel tank;generating a first signal the value of which continuously varies inaccordance with the measured value; averaging the above mentioned signalvalue over predetermined time intervals; generating a second signalcorresponding to the averaged value; calculating a fuel amount inaccordance with the value of the second signal to display the calculatedfuel amount; discriminating vehicle driving condition according to apredetermined parameter; and varying the above mentioned predeterminedtime interval according to the discriminated conditions.
 18. The methodaccording to claim 17, wherein the above mentioned discriminatingparameter for the driving condition is vehicle speed so that the averagevalue of the first signal over a first time interval is generated as thesignal value for the second signal when the vehicle speed is zero, orthe averaged value of the first signal over a second time interval whichis longer than the first time interval is generated as the signal valuefor the second signal when the vehicle is running at a non-zero speed.19. The method according to claim 17, wherein the above mentioneddiscriminating parameter for the driving condition is the "on" or "off"position of the ignition switch so that the average value of the firstsignal over a first time interval is generated as the signal value forthe second signal when the ignition switch is in "off" position, or theaveraged value of the first signal over a second time interval which islonger than the first time interval is generated as the signal value forthe second signal when the ignition switch is in "off" position.